Centrifuge discharge means



March 21, 1967 L. SHAPIRO 3,310,232

CENTRIFUGE DISCHARGE MEANS Filed Dec. 17. 1964 INVENTOR LEONARD SHAPIROBY W ATTORNEY United States Patent ()fiice 3,31%,232 Patented Mar. 21,1967 3,310,232 CENTRIFUGE DISCHARGE MEANS Leonard Shapiro, Upper Darby,Pa., assignor to Pennsalt Chemicals Corporation, Philadelphia, Pa., acorporation of Pennsylvania Filed Dec. 17, 1964, Ser. No. 419,086 4Claims. (Cl. 233-22) This invention relates to centrifuges. Morespecifically this invention relates to centrifuges provided with means'for discharging separated liquids under positive pressure and in amanner that minimizes foaming of the liquids.

The prior art relating to centrifuging is replete with innumerabledischarge devices for removing separated liquid from solid bowlmachines. A common expedient is simply the provision of a ring dam ortube dam over which the separated liquid may spill to the outside of thebowl for collection by a suitable cover device. Alternatively, a skimmertube dips into an inwardly facing trough or pocket mounted on thecentrifuge bowl and scoops the liquid as it races by. In a differentform the skimmer tube takes the shape of a paring disc which is disposedon the centrifuge axis and extends outwardly on all sides into thetrough or pocket. The paring disc is equipped with angled passages intowhich the liquid rushes as the centrifuge rotates. A suitable inwarddischarge channel for the disc is provided.

In the separation of many liquids an essential consideration is theminimizing of turbulence once the liquid is separated. Some separatedliquids are sensitive to such turbulence and may bruise or becomeaerated, undesirably producing a foam. A common example is theseparating of orange juice from seeds, pulp, etc. wherein if the juiceis aerated and foamed it rapidly deteriorates in taste and acquires asharp and disagreeable flavor.

There have been many attempts in the past to minimize foam in the liquiddischarge from a solid bowl centrifuge. One such attempt is documentedin the US. Patent 2,302,168 which issued Nov. 17, 1942. In this patentlips on the inlet openings of the paring device extend outward from thepassages so that the openings are sealed to the entry of foam into thedischarge. While this patent represented a marked advance over the priordevices, the present invention relates to a refinement of the samegeneral type of devicea paring device-and has for an object thereduction of foaming of liquid prior to and during its removal from thecentrifuge.

There is exhibited when any stationary object is submerged in a body ofliquid in a centrifugal field a phenomenon that is known as secondaryflow." Secondary flow is the movement of the liquid out of the liquidbody and up the outside of the stationary object. It arises because athin film of liquid immediately adjacent to the immersed object isstationary with the object, and liquid outward from the film is movingat a velocity of the centrifuge bowl and is therefore under centrifugalpressure. There is hence a tendency for the liquid outward of the filmto displace the film and force it up along the stationary object to andabove the surface of the liquid body. As the liquid leaves theair-liquid surface it also exhibits a tangential velocity componentwhich throws it outwardly away from the stationary object, causing greatturbulence and splashing which entraps air and causes foaming.

Studies of the operation of paring devices for centrifuge liquiddischarge have indicated that the considerable foaming in the liquidabout a paring device is due to secondary flow. The present inventionrelates to means for avoiding turbulence normally developed by secondaryflow of liquid in the indicated situation and for consequently promotinga smooth liquid-gas interface about the paring device. 1

There are, of course, incidental advantages attendant with the smoothingdown of the liquid-vapor interface. For instance, there is the advantagethat the position of the liquid-liquid interface within the bowl may bemore accurately controlled by back pressure on the liquid dischargelines from the paring devices. Further, because the liquid-vaporinterface about the paring device is smooth and no back pressure isneeded simply for the purpose of keeping foam out of the discharge, therange of control attainable by this means is greater than were there adisturbed interface. There is the additional advantage to a smoothinterface: less power is required to drive the centrifuge bowl. Asexplained, there is no need for back pressure on the paring devicemerely to avoid entry of foam into the centrifuge discharge line. Hencethere is less power-consuming pumping necessary by the paring device.Further, with the liquid-vapor interface in smooth condition there isless power-consuming friction between the paring device and the liquidabout it. All of these benefits flow from the present invention.

Other features of the invention will be apparent from a review of thefollowing specification describing a preferred form of apparatus andreference to the drawings in which:

FIGURE 1 is a fragmentary sectional view of a centrifuge embodying theinvention;

FIGURE 2 is an enlarged sectional view taken on line 22 of FIGURE 1; and

FIGURE 3 is a slightly enlarged sectional view of structure withinsection line 33 of FIGURE 1 and indicating a fiow of liquid about partsof the apparatus.

Briefly, in a centrifuge having a discharge paring device comprising acircular structure with passages from its periphery to an inwarddischarge channel, the invention is the provision of at least oneannular rib disposed on -a side of the paring device and adapted toreduce disturbance of the liquid-air interface of the liquid in whichthe device is immersed.

Referring more specifically to the drawings, FIGURE 1 is a fragmentarysectional view of a centrifuge embodying the invention and generallydesignated 10. It comprises a bowl 12 mounted for rotation by asuspending and driving shaft 14. The bowl structure may include a set.16 of frusto-conical discs which are disposed about -a vaned centertube 16a and operate in the conventional manner to increase efficiencyof the separation. The feed liquid is delivered to the lower end of thecentrifuge by feed means (not shown).

Mounted on the top of the bowl 12 is the heavy discharge housing 18 andthe light discharge housing 20. The housing 20 is supported on thedividing cone 22 secured between the upper end of the center tube 16aand the bowl top. Inbetween the dividing cone 22 and housing 18 areaplurality of spaced ribs 24 which space the elements properly andpermit passage of the heavy liquid from the centrifuge bowl into apocket 26 facing inwardly and formed between the housings 1-8 and 20.The ribs widen in the pocket 26 and comprise part of radial vanes 28which assure rotation of the liquid within the pocket 26 with the bowl.

The housing 20 which together with the inward annular wall 30 alsosupported on the dividing cone 22 forms a pocket 32 which is providedwith vanes 34. In operation separated light liquid from the centrifugebowl spills over the annular wall 30 into the pocket 32.

Surrounding the drive and supporting shaft 14 is a stationary dischargeassembly comprising the paring discs 36 and 38. The structure of theparing discs are comparable. As shown in FIGURE 2 the disc.36 is annularand provided with passages 37 which may be curved and extend from theperiphery of the device to an inward discharge channel 40. The channelis formed between 3 the tubular exterior wall 42 of the paring device 36and the tubular wall 44 of the lower paring device 38. Spacing ribs 46are provided to hold the two tubular portions in proper relation.

The-lower paring device 38 similarly has extending inward from itsperiphery discharge passages 48 which extend to the inward dischargechannel 56 between the tubular element 44 and the inner tubular element52. Ribs 54 hold these two parts in proper relative position.

The paring device assemblies are supported as shown on the centrifugecover which is stationary. The upper ends of the passages 40 and 50communicate respectively with discharge conduits 56 and 58 as shown.

Focusing now on the particular area of the invention, it will be notedfrom FIGURE 2 that the opposite faces of the paring device 36 areprovided with spaced annular ribs 60 and 62. These ribs which aredisposed concentrically about the axis of the centrifuge serve (FIGURE3) to deflect outward and into the liquid of the pocket 26, liquid movedinward by the secondary flow phe nomenon. It will be understood that theliquid level is such that some ribs are normally immersed in the liquidin the pocket 26.

Similarly ribs 60' and 62 are provided for the same purpose on theparing device 38.

A splash shield 64 is provided on the underface of the paring device 36and also serves to control turbulence or splashing. Passages 66 throughthe paring disc 36 pro vide means for venting gas pressures which maydevelop on either side of the disc.

FIGURE 3 shows the paring disc 36 as submerged in operation to alternateliquid levels a and b. From the above description of the secondary flowphenomena it will be understood that liquid film adjacent the stationaryparing device is forced by surrounding liquid pressure inward along thesides of the paring device and would tend to create a splash at theliquid level line L. However, due to the presence of the annular ribs 60and 62, the inward flow is deflected laterally into the body of liquid(see arrows) and thus the air-liquid interface remains smooth andundisturbed.

The number of ribs used may, of course, be different from the numbershown on the drawings. The number should not be increased so high thatthere is not sufiicient space to permit free circulation of liquidbetween adjacent ribs. Obviously if the ribs are not sufficiently spacedat primary objective of the invention will be defeated.

It should be understood that variations within the scope of theinvention are possible. For instance the invention may be applied to acentrifuge having a hori zontal axis and to the paring device of acentrifuge of an altogether different type, for instance a wormcentrifuge.

Therefore, it is to be understood that the, above par ticulardescription is. by way of illustration and not of limitation, and thatchanges, omissions, additions, substitutions, ,and/ or othermodifications may be made without departing from the spirit of theinvention. Accordingly, it is intended that the patent shall cover, bysuitable expression in the claims, the various features of patentablenovelty that reside in the invention.

I claim:

1. A centrifuge having a discharge paring device normally immersed inliquid to be discharged and comprising a circular structure withpassages from its periphery to an inward discharge channel, a pluralityof spaced annular ribs disposed on a side of the paring device inwardfrom the periphery thereof and concentrically about the centrifuge axis,whereby the ribs serve to reduce disturbance of the liquid-air interfaceof the liquid in which the device is immersed.

*2. A centrifuge as described in claim 1 including additionally anoutwardly and laterally extending annular splash shield disposed on saidside inward from the ribs.

3. A centrifuge bowl having an axis of rotation, an

annular inwardly facing pocket mounted on the bowl concentric with theaxis of rotation and receiving a discharge liquid from the bowl, thepocket having side walls extending inward to a radial level establishinga maxi mum depth of liquid for the pocket, a stationary takeoff devicehaving a circular outer periphery disposed concentrically about the axisof rotation and extending outward into the pocket, the takeoff devicehaving opposite substantially radial sides and passages from itsperiphery into an inward takeoff conduit, the improvement of at leastone annular rib extending perpendicularly outward from one of said sidesat a position inward from the periphery thereof and disposed concentricwith the axis and at a radius greater than the level.

4. A centrifuge as described in.claim 3 including additionally anoutwardly and laterally extending annular splash shield disposed on saidside inward from the ribs.

References Cited by the Examiner UNITED STATES PATENTS 2,125,453 8/1938Lindgren 233-22 2,197,911 4/ 1940 Andersson 23322 FOREIGN PATENTS 63,7387/ 1945 Denmark. 91,209 6/1961 Denmark.

M. CARY NELSON, Primary Examiner.

HENRY T. KLINKSIEK, Examiner.

1. A CENTRIFUGE HAVING A DISCHARGE PARING DEVICE NORMALLY IMMERSED INLIQUID TO BE DISCHARGED AND COMPRISING A CIRCULAR STRUCTURE WITHPASSAGES FROM ITS PERIPHERY TO AN INWARD DISCHARGE CHANNEL, A PLURALITYOF SPACED ANNULAR RIBS DISPOSED ON A SIDE OF THE PARING DEVICE INWARDFROM THE PERIPHERY THEREOF AND CONCENTRICALLY ABOUT THE CENTRIFUGE AXIS,WHEREBY THE RIBS SERVE TO REDUCE DISTRIBANCE OF THE LIQUID-AIR INTERFACEOF THE LIQUID IN WHICH THE DEVICE IS IMMERSED.